At present, a typical manufacturing method for complicated shapes includes building up a required weight or volume of molding compound by forming a laminate of plies of chopped fiberglass pre-impregnated with a plastic such as a thermosetting synthetic resin which may include a catalyst, plus fillers and the like, and thereafter curing the material in a mold under heat and pressure. The wheel may consist entirely of the molding compound or it may incorporate rigid reinforcing members at points of particular stress.
Cut sheets of molding compound (SMC) may be stacked in the mold in a rosette pattern with overlapping edges, such as described in U.S. Pat. No. 3,369,843 to Prew. Other known patterns for arranging the plies of the charge may be stacks of square, rectangular or circular sheets, simply axially stacked with coinciding edges, or rotated in a radial plane with respect to each other; or in pinwheels, or pyramids. SMC may also be charged as a roll or an annulus placed in the mold with its center line lying in a plane parallel to the mold base. However, the products of these charges tend to exhibit, for example, knit-lines, non-uniformity and voids where spaces between lamina, both radially and axially, originally existed in the charge pattern.